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Re: Sphere/Toroid Comparison Chart

Original poster: "Terry Fritz" <twftesla-at-uswest-dot-net>

Hi Bart,

There is another fun twist to all this.  When a top load is added to a
secondary coil, the voltage profile along the coil changes which affects
the coils effective inductance.  The inductance can actually drop as much
as 20% do to this effect.  See:


for my actual voltage profile measurements and:


for Paul's computer analysis of this.

BTW - Paul's computer analysis was generated long before the actual
measurements were taken which confirmed the models.  Another triumph of
computer modeling :-)))

E-Tesla6 uses voltage profile curve fitting from Paul's TSSP data to
account for this effect.  Those interested should check out the mass of
fascinating information at:


We will be studying the remarkable implications of this work for decades to



>At 08:48 PM 5/8/2001 -0700, you wrote: 
>John, Terry, All, 
>I've tested my two toroids and my measurements "do not" agree with less than 
>20% reduction of Ctop. 
>See below: 
>Tesla list wrote: 
>Original poster: "John H. Couture by way of Terry Fritz 
><twftesla-at-uswest-dot-net>" <couturejh-at-worldnet.att-dot-net> 
>Terry - 
>I entered your coil's data into the JHCTES Ver 3.2 program to see what it 
>comes up with for a toroid. To get the 87.66 Khz the program came up with 29 
>pf for the capacitance. This is about 12% less than the graph shows (space 
>33 pf) for an 8 x 30 toroid. On my web site I mention that the graph 
>capacitance would be reduced about 20% when placed on the TC secondary. It 
>appears this may be too high a percentage. We will have to wait until more 
>data is obtained.
>I've been doing some toroid Fr tests the last couple weeks. 
>Purpose: To measure the change in Fr vs. calc'd with two different toroid 
>dimensions and also to check Ctop against Bert Pool's equations when C 
>is placed on the secondary. 
>Method: Frequency meter (0.1% accuracy at these frequency's) using Terry's 
>TC Tuner. The secondary is set upon a pvc pipe stand (no primary). Toroids 
>are lowered via pulley arrangement to measured distances. Tuner connects 
>between bottom sec. winding and RF ground. Tuner dial is "finely" turned to 
>acquire Fr indicated by led brightness. Tuner is measured with Frequency 
>This may sound a bit odd, but the tuner measurement is within 1kHz of 
>measurements taken via oscope and loop antenna (running) and I checked it 
>against E-Tesla6 (of who's Fr accuracy was less than 1kHz), so the method 
>"is" working. The tuner acts as a device that captures the Fr. Every coiler 
>should build one of these (it's so simple). Great job Terry! 
>Toroids are precise measurements via circumference measurements: 
>Toroid No. 1 = 7.7" x 32" at a calc of 35.2pF. 
>Toroid No. 2 = 6.5" x  37.9" at a calc of 39.2pF. 
>Secondary: 12.75" x 43.25". 
>Toroid No. 1 (7.7" x 32") 
>Level    CalcFr    MeasFr    CalcC     MeasC 
>(inch)    (kHz)     (kHz)     (pF)      (pF) 
>-1        76.8     88.8      35.2       21.0 
> 0        76.8     88.4      35.2       21.4 
> 2        76.8     87.8      35.2       22.5 
> 3        76.8     87.6      35.2       22.1 
> 4        76.8     87.0      35.2       22.7 
> 6        76.8     86.8      35.2       22.9 
> 8        76.8     85.9      35.2       23.9 
> 10       76.8     84.7      35.2       25.2 
>Toroid No. 2 (6.5" x 37.9") 
>Level    CalcFr    MeasFr    CalcC     MeasC 
>(inch)    (kHz)     (kHz)     (pF)      (pF) 
>-1        74.2     82.8      39.2       27.3 
> 0        74.2     82.6      39.2       27.6 
> 2        74.2     82.2      39.2       28.0 
> 3        74.2     81.8      39.2       28.6 
> 4        74.2     81.3      39.2       29.2 
> 6        74.2     81.1      39.2       29.4 
> 8        74.2     80.6      39.2       30.0 
> 10       74.2     79.7      39.2       31.2 
>With Toroid No.1 data, the Fr ranges from 15.6% to 10.3% (closer to 
>calculated Fr as toroid height is raised). Ctop for the toriod ranges from 
>40.3% to 28.3%! That's a affect (possibly due to large coil?). 
>With Toroid No.2 data, the Fr ranges from 11.6% to 7.4%. Ctop for the 
>toroid ranged from 30.4% to 20.4%. 
>Other than the obvious (reacts as one would expect) height changes, 
>something here does standout: 
>Toroid No.1 is larger in cord diam. and smaller in outer diam. Thus, Toroid 
>No.2 is "physically" farther away from the secondary and therefore less 
>affected. Both toroids calc'd capacitances are similar, but toriod 
>"proximity in relation to the secondary" appears to play a major roll in 
>both Fr and Ctop change. 
>I don't see a standard percent value we can throw to this (although anything 
>is better than nothing). I know my secondary is on the large side and might 
>be why my values for Ctop vary far more than 20%. 
>If you have a huge cord size that is "suppose" to have a large Ctop value, 
>you may be better off with a smaller cord size at a wider diameter (not 
>because of the Ctop value, but due to the toroids proximity to the 
>BTW, I also mounted the toriods on top of each other at 3" and 14" 
>distances. By using 50% of each and applying these values to Bert Pools 
>standard toroid equation (as d1 and d2), the accuracy was amazing (3% to 
>0.6% from measured). I also swapped toroids (who was on top) and there was 
>very little change (I didn't expect that). 
>BTW, the above data's toroid height was measured from top secondary winding 
>to bottom plane of toroid. This of course was adjusted for center of toroid 
>when using E-Tesla 6. BTW, at a hieght of 0 on the 7.7 x 32 toroid (or 3.85" 
>for E-Tesla 6), I measured 88.4kHz and E-Tesla 6 predicted 88.49kHz. Pretty 
>good program and Tuner! 
>For E-Tesla 6, wall distance is used, but often times there are objects 
>around that can affect Fr including my own body. One wall was at 80" and the 
>other 3 were more than double that. I used the nearest wall at 80". Amazing 
>program! BTW, ceiling height is 120", and I did "not" include a primary in 
>the program (0 for all primary inputs - worked perfectly and was how I 
>measured the coil). The primary should change results and then possibly Ctop 
>would be in the 20% range or less. Maybe that is the next test. 
>There is a proximity relationship here between toroid and secondary. I can't 
>conclude much until a smaller coil is tested with these same toroids and 
>test parameters (time to wind a 6" diameter coil). 
>Just thoguht I'd share my results. Any thoughts from the list? 
>Take care, 
>Bart A.